Magnetron



P. c. GARDINER 2,906,921

MAGNETRON 2 Sheets-Sheet l Sept. 29, 1959 Filed Aug. 25, 1956 llllllnl ilnllllilllllnllllll! Sept. 29, 1959 P. c. GARDINER MAGNETRON Filed Aug. 23, 1956 2 Sheets-Sheet 2 mvENToR: PAUL c. GARD'INER,

United States Patent O 2,906,921 MAGNETRON Paul C. Gardiner, Scotia, N.Y., assign'or to General Electric Company, a corporation of New York Application August 23, 1956, Serial No. 605,796 14 Claims. (Cl. S15-39.69)

This invention relates to magnetrons and more particularly to novel structure in multiple cavity resonator type magnetrons for reducing undesired mode oscillations and to novel methods for assembling such magnetrons. Y

A type of magnetron in common use is the so-called multiple resonator magnetron which includes a plurality of radial anode extensions or segments which are disposed in juxtaposition around a common center to deiine a plurality of resonant cavities and which cavities are adapted to be electromagnetically coupled. As is well known, magnetrons of the above type will oscillate in several modes corresponding to the various frequencies to be expected from a multi-resonant system whose in-` dividual elements are coupled. In such a magnetron there is a possibility of the frequency jumping from one mode to another during operatiom and in order to insure that the magnetron oscillates in the desired mode, various methods of coupling the resonant structures to suppress the undesired modes have heretofore been employed. Frequency jumping is objectionable in practice for various reasons, primarily because each magnetron and the associated circuitry are designed for most ecient operation `at a particular frequency and the e'ciency of a magnetron is likely to vary considerably between one mode and another. Lower eiciency means lower power output, and more power lost in the magnetron with a consequent increase in heating of the anode and the cathode, causing among other things a shortening of the life of the cathode. Further, the magnetron must be frequency stable at the prescribed frequency to prevent the magnetron from interfering with other radio frequency power sources or receiving means in the vicinity.

In multiple resonant cavity magnetrons the so-called 1r mode of oscillation, in which the adjacent extensions of the resonant cavity anode structure differ in voltage phase by 1r radians or 180 electrical degrees has been found in practice to be thel most desirable mode of oscillation. Because of the objections to oscillations in other than the selected mode, as noted above, efforts are usually directed toward the elimination of all except the 1r mode.

To reduce oscillations in undesired modes and to favor oscillation in the 1r mode, `alternate anode extensions may be connected as a group by conductive members or straps and the anode extensions intermediate the alternate extensions may be connected as a second group by other straps. Alternate ones of the anode extension thus tend to be at the same potential. Since the extensions are coupled in parallel by the straps, slight physical variations in the cavities are nullilied so that the cavities tend to oscillate at one frequency. v i

In the 1r mode of oscillation, the vanes connected as a group should be at one potential; and the vanes conice nected as the second group should be at a potential whose phase is 1r radians displaced from the phase of the rst group of vanes. However, it is not possible to make the straps of zero impedance, so that this expedient of strapping does not entirely prevent operation in modes other than the 1r mode. The finite length of the straps will prevent the extension segments to which the straps are conl nected, to be compelled, in all circumstances, to assume exactly the same potential. Further, since in connecting alternate segments each of the straps passes adjacent to an intervening segment of opposite polarity, there'is a flow of current in each of the strapsdue to the capacitive coupling.

In other than the 1r mode, the various points on the straps are at different potentials, so there will be a net current flow along the straps of magnitude depending on the potential dilference between various points on the strap and the distributed inductance and capacitance of the straps. If the straps connecting the two groups of vanes are adjacent to each other, the straps act as a reentrant line which is resonant at `a wave length other than the wavelength of the magnetron, and which can result in producing undesired oscillations. Cutting or breaking the straps has 'heretofore been employed as a means for injecting a discontinuity to prevent resonance of the straps at a frequency within the magnetron range. However, cutting the straps is undesirable due to the fact that a cut strap is mechanically unstable and weak and is difficult and expensive to assemble.

Accordingly, it is a principal object of the present invention to provide novel coupling means for the anode structure of multiple cavity resonator type magnetrons to reduce and prevent oscillations in undesired modes'.

With the ever increasing demand for higher frequencies and higher powers of operation vand because of the desirability of using magnetrons of the multiple resonant cavity type for this purpose, there has ibeen evidenced a decided need for simplified magnetron structures which permit facility in factory production and which afford improvements inthe operating characteristicsv of the devices of this type.

Accordingly,- it is another object of the present invention to provide a magnetron structure which simplifies final assembly of said magnetron.

In. the attainment of the foregoing objects,y I provide novel coupling means for multiple resonator type magnetrons including straps which couple in chordal relation to the circular straps connecting the anode extensions, and a plurality of inductive output coupling loops disposed adjacent said anode extensions for interrupting undesired mode oscillations. Further, I provide a novel and economical magnetron construction in which three main subassemblies are separately formed and adapted to permit eicient final assembly of the magnetron.

Other objects and advantages will become apparent after a consideration of the specification and the drawings in which:

Figure 1 is an -axial cross sectional view of a magnetron in accordance |with my invention;

Figure 2 is a cross sectional view taken along line 2 2 of Figure 1;

Figure 3 is an isometric View of the strap conductors and the chordal straps in accordance with my invention;

Figure 4 is a reduced exploded view of the magnetron of Figure l; and

Figure -5 is an isometric fragmentary view of the output coupling loops of Figures 1 and 4 in accordance with my invention.

ln Figure 1 my invention is illustrated as applied to an ultra-high-frequency magnetron having a metallic cylindrical tubular envelope 11 of, for example, a copper clad steel material. Within the envelope 11 and approximately at its central region there is provided an anode. structure 17, preferahly of copper, and which inclttds an annular member or sleeve 19 for attaching the anode structure 17 to the envelope 11. The anode structure 1.7 consists of a plurality of extensions or vanes, two of which are shown at 7a and 7j, which extend radially inwardly from sleeve 19 and terminate in a eentral interaction space 30 within which a cathode 23 is located. For purposes of clarity in the drawings, the vanes other than 7a and 7) are not shown in Figure 1. These are, however, Shown in Figure 2 at 7b through 7e and 7g through 7j. Centrally apertured cup-shaped metallic ang'ed members 13 andV 15 are welded or otherwise hermetically joined to the inside walls of envelope 11 to support the cathode-lead and exhaust tubulation elements, respectively, which elements, in turn, serve also to close the opposite ends of the envelope 11, as will appear. i

To establish the magnetic eld necessary for operation of the magnetron, I employ magnetic means which include a pair of electromagnetically magnetized pole pieces and 27 located within envelope 11 and affixed to flange members 13 and 15 respectively. (Pole pieces 25 and y27 may be energized by any suitable conventional means, not shown.) Permanently magnetized pole pieces may be employed instead of the electromagnetically magnetized pole pieces 25 and 27. Pole pieces 25 and 27 are spaced longitudinally along the axis of the envelope 11 a predetermined distance from anode 17 by spacer members 24 and 26. Two end spaces 18 and 18 are dened between pole pieces 25 and 27 respectively, and the anode structure 17. During operation, magnetic ux existing vin end spaces 18 and 18' mutually couples the various cavities. Uniformity of the magnetic eld in the interaction space between the cathode 23 and the anode vane extremities or faces 28 is provided by forming the center portion 'of each of the pole pieces 25 and 27 in frusto-conical shape. Pole piece 25 has an aperture in the center thereof through which extends a rod member 33 and a support member 37 which members serve as the electrical connections as well as mechanical supports for `cathode 23. For purposes of symmetry, 7central aperture 22 may also be formed -in pole piece The `cathode 23 which may be a directly heated thermionic helical filament, as shown, or an indirectly heated cathode, is located centrally within the envelope 11 and in cooperative relation to the anode structure 17. A conductive rod 33 is located concentric within cathode 23 and provides means for centering and positioning the cathode 23. Disks 29 and 31 are axed to opposite ends of cathode 23 to prevent electrons from leaving the interaction space 30 and provide vstructure for mechanically supporting 'and electrically coupling to the cathode. Disk 29 is 'aixe'd to one end of rod 33 and disk -31 has a central aperture through which the rod passes. The oppostte end'of rod 33 is inserted and sealed in an electrical terminal member 35, which in turn 'is atixed through conductive support 41, insulator 43, and metallic sup- -port to cylindrical member 39 which serves as the other electrical terminal for lcathode 23. Member 39 couples electrically through conductive member l37 and d1sk 31 to cathode 23. Member 39 is alixed through metallic member 48, 'to'outer insulator 47 and flange member 13 to the envelope 1v1. Terminal member -35 couples to one side of the 'alternating current voltage vsource 42 which energizes cathode 23, and also couples to the negative side of the high voltage anodes'ource 44. The voltages indicated in 'Figure lare merely illustrative and suitable voltages of other magnitudes may be emplOYed- The output is taken from the magnetron 1l) through VContact with alternate vanes. `to a'second group of vanes, say vanes 7b, 7d, 7f, 7h and 4 l inductively coupling loops 51 and 53 which extend into the end space 1S to extract high frequency energy from the magnetron. It will be noted that no physical contact is effected between loops 51 and 53, on the one hand and the anode structure 17 on the other. This feature is productive of certain major advantages, as will appear. One end of each of the loops 51 and 53 is affixed to pole piece 27 as more clearly shown in Figure 5. The loops 51 and 53 are generally U-shaped, with one leg portion thereof passing through apertures 20 in pole piece 27 and the opposite ends of each of the loops being aixed to the periphery of -an apertured plate 55. Plate 55 is connected and electrically coupled through conductive member 57 and connector 59 to the inner conductor of an output coaxial line, not shown. Plate 55 is affixed through conductive support members 57 and 61, and insulator 63 to harige member 15. The outer conductor of the output coaxial line is adapted to be positioned adjacent to, and to contact the surface of ange 15. A copper or other material exhaust tube 38 is suitably disposed in the aperture of plate 55 and aixed to the platc. A-fter the air and gases are extracted during the evacuation process the magnetron 10 is vacuum sealed by sealing the end 32 of tube 38 in any convenient manner.

Circular or ring strap members 65, 67, 69 and 71 of a conductive material are axed to opposite sides of the anode structure 17 and will be discussed in more detail hereinbelow in conjunction with chordal strap 73, 75, 77 and 79, which chordal straps are aihxed Vto the ring strap members 65, 67, 69 and 71, respectively. In order that the chordal straps may be afiixed to their respective ring straps without contacting the other straps, the free ends of the inner straps 65 and 69 are non-coplanarly disposed relative to the free ends of the outer straps 67 and 71.

Flange member 49 aflixed to envelope 11 provides a means of supporting the magnetron and also as a means of electrically grounding the positive side of the anode voltage source. Tubular member 50 on the periphery of envelope 11 adjacent the anode structure 17 provides a conduit for liquid coolants.

As shown more clearly in Figure 2, the anode structure 17 which consists of inwardly extending radial-type vanes 7a-7j inclusive, is characterized by a plurality of space resonant regions or cavities Srl-8j which are adapted 'to be energized by the rotating space charge established in the 'interaction region 3i) in a manner well known to those skilled in this art. The number of radial vanes 7a-7f and the thickness thereof are chosen to provide high-frequency, high-power-level operation. Ten vanes 7a-7j are disclosed in the embodiment herein described. However, this number is Amerely illustrative and not to be taken as restrictive. The inner extremities or faces 28 of the Vvaines 741-71' next adjacent to the cathode structure23 are tapered s'o as to provide gaps 32 of predetermined width to provide a predetermined desired degree of coupling between the cavities Srl-8j and the interaction space 30. `Circular conductive straps 69 and 71 are connected alternately to each of the anode vanes 7a-7j, preferably as close to the faces 28 of the vanes 7rz-7j as mechanical expendiency will permit. As shown more clearly in Figure 3, the ring conductors, for example, conductors 69 and 71 are supported and affixed to the respective vanes by step extensions or pedestals 70 -and 72, respectively, formed on the inner ends of the rings Aso that the outer ends of the rings are disposed in non-coplanar relation.

Referring again to vFigure 2, it will be noted that strap 69 is affixed to one group of vanes, say vanes 7u, 7c, 7e, 7g, and 7i, by the extensions 70 and thus is in electrical Strap 71 is similarly aflixed 7j by step extension 72 and thus is in electrical contact with -the vanes intermediate the vanes interconnected by strap 69. Ring straps and 67at the opposite end of the anode structure 17 couple similarly to vanes 711-71'.

The two groups ofl vanes are preferably symmetrical with respect to electrical ground reference in order that the vanes have the same capacity and inductance to ground, and so that any current ilow in the two groups of vanes is the same. To promote electrical symmetry the inner strap 65 is connected to those vanes to which outer strap 71 on the opposite end of anode 17 is connected and conversely outer strap 67 is connectedl to those vanes to which inner strap 69 is connected.

Undesired modes, in strapped magnetrons, partially depend on strap length and strap capacitance. For disrupting the aforementioned rotating undesired-mode elds, I provide strap members 77 andv79 aiiixed in chordal relation to circular or ring-strap conductors 65, 67, 69 and 71. The chordal straps connected to each pair of ring straps on the same side of the anode vanes 7a-7j, for example, straps 77 and 79, are disposed in spaced parallel relation to one another and are aixed across the respective circular strap and not connected with the other strap or with any otherconductor, Figures 2 and 3.

-In resonant cavity magnetrons the radio frequency iield of certain undesired modes, for example, the (n-l) mode where n is 1/2 the number of resonators which can be considered as the closest proximate mode to the 1r mode changes in relation with the electron motion. The iield lines may be considered as rotating in relation with the electron motion. The circular strap pairs on each side of the anode 17 can be thought of as a parallel conductor line carrying an electrical wave, corresponding to the field lines of force. lf the (n-1) mode eld isto be supported it must rotate in predetermined phase relation such that each of the cavities reinforce the (n-l) mode eld in the proper phase and time relation. By employing the strap arrangement of the invention, the rotating undesired (n-l) mode asv it travels around the circular straps sees two conductive paths, one path completely around the circular straps 69 and 71, Figures 2 and 3 Vand a second path partially around the straps 69 and '71 and through the chordal conductive straps 77 and 79. The path across the chordal straps 77 and 79 is of a length shorter than that required to conduct the rotating eld in proper time and phase relation with the cavities. The straps 65, 67, 73 and 75 on the opposite side of the anode structure 17 function in a similar manner. The shorter conductive path causes the rotating mode to get out of phase with the energy supplied by the cavities Saz-8j and hence fails to support the undesired oscillations. Due to the shorter-path straps the undesired mode eld will tend to change phase and even to buck or short circuit itself. The 1r mode eld will not be adversely affected since, in the 1r mode of operation, each of the straps should be, at the same potential throughout its surface. Thus, all modes other than 1r Inode tend to be suppressed or disrupted.

-In the practical embodiment herein desired, a single conductive strap, say strap 77 is aixed in chordal relation to one of the circular straps say strap 69, and similarly chordal strap 79 isl affixed to strap 71. The chordal straps aiiixed to each pair of ring straps, for example, straps 77 and 79, areA preferably disposed in spaced parallel relation. While the chordal Vstraps can, if desired, be aixed diametrically across the ring straps Iwith satisfactory results, I have observed that the chordal straps operate more satisfactorily when radially displaced from the cathode 23 region. Hence, other than diametrically placed straps are generally preferable.

If desired, two or more chordal conductors can be aflxed across each of the ring straps, or chordalstrap pairs can be employed which are disposed to criss-cross the ring straps. Satisfactory results may also be obtained by having chordal straps affixed to only one pair of ring straps, for example, ring pair 65 and 67, with a consequent advantage of more economical construction.

To further reduce undesired mode oscillation, the pair of output coupling loops 51 and 53 are disposed to extend into end space 18 in radial relation to the axis of the tube 11, Figure l. The coupling loops are aixed to pole piece 25 andare predeterminedly spaced from the anode structure 17 by means of spacer 26 which abuts against the pole piece 25.- Positioning the coupling means in end space ,18' -provides frequencyselection which is highly discriminatory, and the use of a plurality of loops provides good coupling engagement with the oscillating modes without requiring that the loops be disposed too close to, or in physical contact with, the anode structure 17. The fragmentary viewof Figure 5 shows somewhat more. clearly the relative position of the coupling loops 51 and 53 the effective planes of which form an angle of 72 circumferentially. The loops 51 and 53 are positioned adjacent alternate anode vanes for maximum coupling engagement. Two or more coupling loops are necessaryfor loading out, that is, absorbing the power, of any undesired modes which might tend to exist within the magnetron 10. In the 1r mode of oscillation, alternate anode vanes are at the same potential, therefore a plurality of coupling out loops placed adjacent alternate vanes will not adversely affect coupling out of the 1r mode energy. Each loop causes not only the coupling out of power of the 1r mode, but also forces coupling-out engagement with the components of undesired modes which might tend to be formed, particularly the (n- 1) mode. By employing two or more space coupling loops any circulating undesired modes close to the magnetron operating frequency Vwhich might tend to be formed will pass at least one of 4the coupling loops at other than minimum current and will be loaded out. If only one loop is employed, a circulating undesired mode may pass the coupling loop at minimum current resulting in the undesired mode not being loaded out.

Two coupling loops provide excellent output coupling as Well as satisfactorily suppressing undesired modes. A larger number of coupling loops might be used to load out the undesired modes still more completely; however, the use of two loops provides the desired results together 'with the benefits of economical construction.

A further advantage of apparatus built in accordance with my invention is the simplified construction which lends itself readily to factory production methods and apparatus. In one practical embodiment three main subassemblies are employed, consisting of a cathode-end subassembly 12, a center sub-assembly 14, and an output end sub-assembly 16. See Figure 4.

The cathode-end sub-assembly 12 includes the ange member .'13, pole piece 25, and the cathode 23 structure. The center or anode sub-assembly 14 includes the cylindrical envelope 11 within which is located the anode structure 17. Flange 49 and conduit 50 may be aiixed to the envelope 11 either beforeor after the final assembly operation. The output-end sub-assembly 16 includes ange member 15, pole piece 27, coupling loops 51 and 53 and the connector 59 which couples to the output coaxial line. l

In final assembly, the cathode sub-assembly 12 and the output sub-assembly 16 are inserted into the respective ends of the center assembly 14 and an argon weld made around the thin edges to aix the sub-assemblies together. Such a smplied assembly is made possible because the output coupling loops are external and physically unconnected to the cathode-anode region. Another advantage in this construction is that no internal electrical connections have to be made during the final assembly. Further, such a construction permits simplied installation of the magnetron in its operational environment in that the output line extends in an axial direction from the magnetron and no output connections have to be made radially into the cylindrical envelope 11.

As seen from Figures l, 4 and 5 the coupling loops 51 and 53 are supported entirely from the pole piece 27 and externally of the anode-cathode region. Thus, pre-adjust- 7 ment of the coupling loops 51 and 53 to give the desired degree of coupling to the anode vanes 7a-7i prior to final welding together of the magnetron 10 may be easily and conveniently obtained merely by rotating the outputend assembly 16.

While specilic examples have been given in describing details of this invention, it will be understood that they have been given merely by way of illustration and that the invention is not limited thereto.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. An electric discharge device of the magnetron type comprising a plurality of electrode extensions detining a plurality of resonators, a first conductive strap conducr tively interconnecting alternate ones of said electrode extensions, a second conductive strap having an electrical length different from the electrical length of said first strap and conductively interconnecting spaced portions of said iirst conductive strap whereby rotating undesired mode fields which might tend to be formed during operation are suppressed.

2. An electric discharge device of the magnetron type comprising a plurality of electrode extensions detining a plurality of resonators including a pair of conductive straps affixed in circular concentric relation, each of said circular straps conductively interconnecting alternate ones of said electrode extensions, a chordal strap conductively connected between circumferentially spaced portions of each of said circular straps whereby rotating undesired mode elds which might tend to be formed during operation are suppressed.

3. An electric discharge device of the magnetron type comprising a substantially closed annular envelope, a plurality of co-operating electrodes within said envelope including a cathode and an open-ended anode structure surrounding said cathode, said anode structure comprising an annular envelope portion and a plurality of extensions directed radially inwardly from said annular portion, the inner ends of said extensions and said cathode bounding a substantially annular interelectrode space, means coupling together the cavity resonators denedby said extensions, said means comprising on each end of said anode structure a pair of annular metallic rings,.one of said rings in each of said pair being conductively connected to alternate extensions, the other of said rings in each said pair being conductively connected to the extensions intermediate said alternate extensions, conductive strap members aflixed in chordal relation to each of said rings, and at least two inductively coupling loops disposed in spaced relation to one another and to said anode structure and extending substantially parallel to the axis of said annular envelope portion in an end spaced between an end of said envelope and said anode structure for abstracting energy from said magnetron, said chordally alxed straps and said plurality of coupling loops eecting a reduction of undesired mode oscillations in said magnetron.

4. An electric discharge device of the magnetron type comprising a substantially closed metallic annular envelope, a plurality of cooperating electrodes within said envelope including a cathode and an open-ended anode structure surrounding said cathode, `said anode structure comprising an annular envelope portion and a plurality of extensions directed radially inwardly from said annular portion, the inner ends of said extensions and said cathode bounding a substantially annular interelectrode space, means coupling together the cavity resonators defined by said extensions, said means comprising on each end of said anode structure a pair of annular metallic rings, one of said rings in each of said pairs being conductively connected to alternate extensions, `the other of said rings in each said pair being conductively connected to the extensions intermediate said alternate extensions, and strap means ai-lixed in chordal relation to at least one pair of Vsaid rings whereby Vundesired-mode fields are disrupted.

5. An electric discharge of the magnetron type comprising a substantially closed annular envelope, a plurality of cooperating electrodes within said envelope including -a cathode and an open-ended anode structure surrounding said cathode, an end member in at least one end of said envelope and spaced longitudinally from said anode for dening an end space therebetween, said anode structure comprising an annular envelope portion and a plurality of extensions directed radially inwardly from said annular portion, the inner ends of said extensions and said cathode bounding a substantially annular interelectrode space, and at least two inductively coupling loops disposed in spaced relation with one another and extending through said end member substantially parallel to the axis of said annular envelope portion and into said end space in spaced relation to said anode structure for inductively abstracting energy from said magnetron, said plurality of coupling loops effecting a reduction of undesired mode oscillations in said magnetron.

6. An electric discharge device of the magnetron type comprising a substantially closed metallic annular envelope supporting an output line at one end, a plurality of cooperating `electrodes within said envelope including a cathode and an open-ended anode structure surrounding said cathode, said anode structure comprising an annuler envelope portion and a plurality of extensions directed radially inwardly from said annular portion, the inner ends of said extensions and said cathode bounding a substantially -annular interelectrode space, magnetic members'extending across both ends of said annular envelope forming a space of relatively high concentration of magnetic ux between each of the magnetic members and said anode, one of said magnetic members having apertures formed therein, a plurality of inductive coupling loops comprising conductive strips having the inner ends thereof a'ixed directly to said one magnetic member and the other ends extending outwardly of the space between said one magnetic member and said anode through the apertures in said one magnetic member and coupling to the output line, said loops being disposed in spaced relation to said anode structure and to each other whereby energy is inductively abstracted from said device and undesired modes are loaded out and suppressed.

7. A magnetron assembly comprising a multiple resonator sub-assembly of a substantially cylindrical envelope having a plurality of anode extensions directed inwardly within said envelope and delining a central annular space, a cathode sub-assembly including a metallic closure for one end of said resonator sub-assembly and including a cathode adapted to be inserted into said annular space, a magnetic member extending across said cathode subassembly and forming the major portion of said end closure, an output sub-assembly including a metallic closure for the opposite end of said anode sub-assembly and having a central conductor, a magnetic member extending across said output sub-assembly in insulative relation with said central conductor and forming the major portion of said opposite end closure, said end sub-assemblies being positioned in respective ends of said anode subassembly to dene spaces between each of said magnetic members and said anode extensions which spaces during operation of said magnetron have relatively large concentration of magnetic flux, and -a plurality of inductively -coupling output loops comprising discrete elongated conductive elements each having one end thereof aliixed to said second magnetic member and the other end extending through said second magnetic member in spaced relation therewith, and said elongated conductive elements including intermeidate bight portions extending into the space defined by said second magnetic member and said anode extensions in spaced relation to said anode extensions.

8. An electric discharge device of the magnetron type comprising a substantially closed annular envelope, a

9 plurality of cooperating electrodes within said envelope including a cathode and an open-ended anode structure surrounding said cathode, said anode structure comprising an annular envelope portion andy a plurality of extensions directed radially inwardly from said annular portion, the inner ends of said extensions and said cathode bounding a substantially annularv interelectrode space, means coupling together thecavity resonators defined by said extensions, said means comprising on each end of said anode structure a pair of annular metallic rings, one of said rings in each of said pair being conductively connected to alternate extensions, the other of said rings in each said pair being conductively Iconnected to the extensions intermediate said alternate extensions, conductive strap members 'ajiixed in chordal relation to said rings, magnetic members disposed within said envelope adjacent the opposite ends of said anode structure for establishing a magnetic field in the region of said cathode and anode, each of said magnetic members disposed to define an end space between said magnetic member and said anode structure, and at least two output loops having the inner ends thereof aixed to one of said magnetic members extending substantial-ly parallel to the axis of said annular envelope portion and into the respective end space in spaced lrelation to said anode for abstracting energy from said magnetron, and for suppressing oscillations in undesired modes.

9. An electric discharge device of the magnetron type comprising a substantially closed metallic annular envelope, a plurality of cooperating electrodes within said envelope including a cathode and an open-ended anode structure surrounding said cathode, said anode structure comprising an annularenvelope portion and a plurality of extensions directed radially inwardly from said annular portion, the inner ends of said extensions and said cathode bounding a substantially annular interelectrode space, means coupling together the cavity resonators defined by said extensions, said means comprising a pair of annular metallic rings aixed to each end of said anode structure, one of said rings in each of said pair being conductively connected to alternate extension, the other of said rings in each said pair being conductively connected to the extensions intermediate said alternate extensions, and strap means aixed in chordal relation to at least one pair of said rings and conductively disconnected from all other elements in said devi-ce whereby undesired-mode elds are disrupted, a chordal strap aixed to one of said rings in each said pair disposed in parallel relation to a corresponding chordal strap aixed to the other said ring of said pair.

10. An electric discharge device ofthe magnetron type comprising a substantially closed annular envelope, a plurality of cooperating electrodes within said envelope including a cathode and an open-ended Ianode structure surrounding said cathode, said anode structure comprising an annular envelope portion and a plurality of extensions directed radially inwardly from said annular portion, the inner ends of said extensions and said 'cathode bounding a substantially annular interelectrode space, a magnetic pole member extending across each end of said envelope in spaced relation with said cathode and anode extensions, an output line carried at one end of said envelope, means coupling together the cavity resonators defined by said extensions, said means comprising on each end of said anode structure a pair of annular metallic rings, one of said rings in each of said pair being electrically connected to alternate extensions, lthe other of said rings in each said pair being electrically connected to the extensions intermediate said alternate vanes, and at least two individual generally U-shaped inductively coupling output loops extending into the end space between one of said magnetic pole members and the anode extensions and spaced from said anode, each loop having the shorter end thereof'aflixed to said one magnetic pole member and the other end thereof extending through said one magnetic pole piece and coupled to said output line.

11. An electric discharge device of the magnetron type comprising a plurality of electrode extensions defining a plurality of resonators, la circular conductive strap conductively secured to alternate ones of said electrode extensions, a chordal'conductive strap conductively connected to only said circular strap and extending between circumferentially spaced portions of said circular strap for effecting shortening of the electrical path 4between said spaced portions, whereby rotating undesired mode fields which might tend to be formed during operation are suppressed.

l2. An electric discharge device of the magnetron type comprising a substantially closed annular envelope including an output line conductor at one end, a plurality of cooperating electrodes withinsaid envelope including a cathode and an open-ended anode structure surrounding said cathode, said anode structure comprising an annular envelope portion and a plurality of extensions directed radially inwardly from said annular portion, the inner ends of said extensions and said cathode bounding a substantially :annular interelectrode space, an apertured magnetic pole piece extending across said one end of said envelope and defining an end spa-ce between said pole piece and anode structure, means coupling together the cavity resonators defined by said extensions, said means comprising on each end of said anode structure a pair of annular metallic rings, one of said rings in each of said pair being conductively connected to alternate extensions, the other of said rings in each pair being conductively connected to alternate extensions intermediate said alternate extensions, a conductive strap extending across and yconductively secured to circumferentially spaced portions of each of said rings only, and at least two discrete inductively coupling loops disposed in spaced relation to one another and extending substantially parallel to the end of said annular envelope portion into said end space in spaced relation to said anode structure for abstracting energy from said magnetron, said loops comprising generally U-shaped strips and each hav- `ing one end conductively secured to said pole piece and the other end extending through said pole piece and conductively secured to said output line conductor, said straps aixed between said spaced portions of said rings and said plurality of coupling loops effecting 1a reduction of the undesired mode oscillations in said magnetron.

13. An electric discharge device of the magnetron type comprising an envelope containing -a cathode and an open-ended anode structure surrounding said cathode, an apertured magnetic pole piece extending across one end of said envelope in spaced relation to said anode structure, an output-line conductor mounted in the end of said envelope containing said pole piece, and at least one discrete generally U-shaped inductively coupling strip extending in the space between said pole piece and anode structure in spaced unattached relation to the latter and with one end conductively secured to said pole piece and the other end extending through the aperture in said pole piece and `conductively secured to said output-line conductor.

14. A magnetron assembly comprising a multiple resonator sub-assembly comprising a substantially cylindrical metal envelope section carrying an anode structure including a plurality of radial extensions defining a central space, a cathode sub-assembly including means closing one end of said resonator sub-assembly, and supporting a cathode centrally in said central space, lan output subassembly comprising a 'metal flange adapted for being joined to the end of said envelope section opposite said lcathode sub-assembly, said ange carrying a centrally disposed output-line conductor and an apertured magnetic pole piece extending thereacross in insulative relation with said conductor, said pole piece being spaced from said anode structure when said flange and envelope section are joined, and at least one. discrete generally U-shaped inductive coupling strip supported solely from said output sub-assembly and in spaced relation with said anode structure, saidV inductive coupling strip having one end conductively secured to the surface of said pole piece facing said anode structure and the other end extending through the aperture in said pole piece and conductively connected to said output-line conductor.

References Cited in the le of this patent UNITED STATES PATENTS Spencer v Feb. 7, 1950 Brown Feb. 14, 1950 Anderson Jan. 13, 1953 Shelton Oct. 18, 1955 Posthumus Oct. 18, 1955 

